There are many kinds of image display devices, e.g., a television, a personal computer, a projector, a video camera, and a cell phone; however, such conventional image display devices are limited in their display size, and thus such a wide range of image as is actually viewed by human eyes has not been able to be obtained from such displays.
On the other hand, as portable displays, an eyeglass type display and a head mount type display, both called a wearable display, are known. As a wearable display, there is known a method in which, as shown in FIG. 28(a), small half mirror 40 is arranged at a portion of the field of view, and an image outputted from image output device 39 such as a plasma display or a liquid crystal is, via projection optical system 38, deflected by half mirror 40 and is projected onto the retina of the eyeball. This method uses the half mirror and thus is such a system (the first type) as the image outputted from image output device 39 is viewed as floating in a portion of the field of view. However, as the field of view angle, a few degrees can only be obtained. As the application of this type wearable display, presentation of the image information of a cell phone has been conceived, for example.
On the other hand, as a method to obtain a little larger image information, there is a system as shown in FIG. 28(b). In this method, a large optical element 41 is arranged before the eyeball, and the image outputted from image output device 39 is, via a plurality of reflecting surfaces and projection optical system 42, projected onto the retina of the eyeball. While with respect to this type of method, a relatively large field of view angle (about 15 to 22.5 degrees) can be obtained, only the type in which the field of view is completely obstructed has been proposed. Thus, as the applicable method thereof, there have been proposed a system (the second type) in which this type image display device is detachably disposed before one eye and is used as a display as a wearable personal computer, and a system (the third type) in which the same image display devices are each independently positioned before each of the eyes and are used instead of a television or a projector.
The above-described three types of the prior art image display devices were respectively expected to substitute, as a wearable display, the cell phone, the notebook computer, and the television or the projector. However, as a matter of fact, while they have the advantage of wearableness, they do not differ much from the conventional display devices with respect to the size of the display field of view, and when considering the bother of wearing them, the eyestrain with the field of view being obstructed, and the weight to be supported by the ears or the head, they have the disadvantage that they are featured in conspicuous defects. Furthermore, even in the case of the display devices having a large field of view angle, the field of view angle is in the range of about ±15 to ±22.5 degrees, and thus a sense of realism could be obtained.
On the other hand, as systems describing the method to obtain a large field of view by allowing the weight to increase and by using a plurality of lenses as the eyepiece, there are, for example, such systems as described in Japanese Unexamined Patent Publication No. 7-244246 or Japanese Unexamined Patent Publication No. 2001-311910, and in such systems, a field of view angle of ±22.5 degrees or more can be realized. However, such systems have a wide field of view angle only in the condition that the eyeball does not move, and neither the shift of the crystalline lens from the eyepiece center that occurs when the eyeball moves nor the associated chromatic aberration is sufficiently taken account of.
In addition, with respect to these kinds of devices having a large field of view angle, because the eyepiece optical system becomes large-sized, resulting in the weight increase, and thus there arises the disadvantage that such devices no longer meet the weight requirements of the HMD type display supported by the head or of the eyeglass type display of which weight is supported by the nose and the ears like eyeglasses.